1. Field of the Invention
The present invention relates to a semiconductive belt which can be used in an image forming apparatus using an electrophotographic system such as a copy machine and a printer, and relates to an image forming apparatus using the semiconductive belt.
2. Description of the Related Art
In an image forming apparatus using an electrophotographic system, first, a uniform electric charge is made on an image carrier surface of a photoconductive photoreceptor made of inorganic or organic materials, and an electrostatic latent image is formed by a laser or the like modulating an image signal, and the electrostatic latent image is developed by a charged toner, and a visualized toner image is formed. The toner image is electrostatically transferred on a transfer material such as recording paper either directly or through an intermediate transfer medium, and is fixed, and a desired image is obtained.
In particular, an image forming apparatus transferring in two steps is known, in which a toner image formed on an image carrier is transferred primarily on an intermediate transfer medium, and the toner image on the intermediate transfer medium is transferred secondarily on a recording paper (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 62-206567).
In the image forming apparatus employing the intermediate transfer medium system, the intermediate transfer medium is a conductive endless belt made of a thermoplastic resin, such as a polycarbonate resin, PVDF (polyvinylidene fluoride), polyalkylene phthalate, PC (polycarbonate)/PAT (polyalkylene terephthalate) blended material, ETFE (ethylene tetrafluoroethylene copolymer)/PC, ETFE/PAT, PC/PAT blended materials, and others (see, for example, JP-A No. 6-095521, JP-A No. 5-200904, JP-A No. 6-228335, JP-A No. 6-149081, JP-A No. 6-149083, and JP-A No. 6-149079).
As a semiconductive belt used for an intermediate transfer belt or a transport belt, an intermediate transfer belt formed by dispersing a conductive filler in a polyimide resin excellent in mechanical characteristics and heat resistance is proposed (see, for example, JP-A No. 5-77252 and JP-A No. 10-63115).
However, since the above-mentioned intermediate transfer belt is high in hardness, it is inferior in toner transfer property, and recently color paper or special paper having an undulated surface by embossing comes to be used, and since following property of the belt with respect to such paper is especially poor, toner transfer property thereof is extremely inferior.
As the rubber belt used in the image forming apparatus employing the intermediate transfer medium system, an elastic belt with a reinforcing material formed by laminating a polyester or other woven material and an elastic member is proposed (see, for example, JP-A No. 9-305038 and JP-A No. 10-240020). However, the elastic belt with a reinforcing material has problems of color deviation due to creep deformation of the belt material over time.
Multilayer belts are also proposed, such as a multilayer endless belt made of plastics, or a belt having a polyolefin urethane layer applied on the surface of a rubber belt (see, for example, JP-A No. 11-24428 and JP-A No. 11-45015).
However, since the multilayer endless belt made of plastics is high in hardness as the case described above, the toner transfer property is poor, and recently color paper or special paper having an undulated surface by embossing comes to be used, and since following property of the belt with respect to such paper is especially poor, toner transfer property thereof is extremely inferior. Besides, since stress on the belt is heavy, the toner is likely to be broken, toner filming on the belt occurs, and it is inferior in durability.
The belt having a polyolefin urethane (which is a thermoplastic elastomer) layer applied on the surface of a rubber belt is a belt formed by spraying the polyolefin urethane on the rubber belt, and thus fluctuations of coat film thickness occur in the plane direction, and the dimensional accuracy is low. Still worse, polyolefin urethane is large in waste (deformation by aging), and adverse effects are caused on copy images.
Another proposal is a two-layer belt using thermosetting urethane resins, having a surface layer made of a thermosetting urethane resin with JIS A hardness of 30 to 70 degrees, and a substrate made of a thermosetting urethane resin with JIS A hardness of 75 degrees or more (see, for example, JP-A No. 2001-282009), by which a favorable transfer image quality is obtained using paper with low surface smoothness.
However, when the surface layer is made of an elastic member of a thermosetting urethane resin, microslip occurs between it and the opposite image carrier, and color registration deteriorates. Further, as the substrate, the thermosetting urethane resin with high hardness is used, and since the Young's modulus is lower as compared with resin materials, the belt thickness must be increased in order to obtain enough strength. As a result of increasing the thickness of the substrate, surface layer deformation increases at the roll bend portion, and the surface layer deteriorates in a long time of use, and favorable transfer image quality becomes unobtainable.